Re: Using Cairo and getting data back out.

["John Hobbs" <john velvetcache org>]

I agree!  That is a decidedly non-trivial solution, and though it's
now in the list archives, I think it should be somewhere more obvious.

We could start some kind of database of little snippets of gtkmm code
like that.  What do you think? Make it cover multiple libraries? Maybe
mm-snippets.org?

For the maintainers, does that sound like a useful thing or something
counter productive?  I'd be happy to write and run it, no sweat off
your backs.  I'll even watch the list closer for useful things, I read
it pretty regularly anyway.  I've gotten so much out of gtkmm I'd like
to give back a little.

Thoughts?

- John Hobbs

john velvetcache org

P.S. I first sent it straight to you Chris, I apologize. Gmail is my enemy.

> On Tue, Aug 12, 2008 at 2:38 PM, Chris Wilson
> <christopher g wilson gmail com> wrote:
>> Glad I could help. It took me a long, long time (~3 days working on it
>> nearly non-stop) to figure that one out.
>>
>> Since it actually is pretty useful, perhaps I should get around to adding it
>> to some documentation...  Anyone agree?
>>
>> We'll see how much free time I'll get in the next week.
>>
>> --Chris Wilson
>>
>> On Tue, Aug 12, 2008 at 9:45 AM, John Hobbs <john velvetcache org> wrote:
>>>
>>> That works brilliantly.  Thank you very much. I never would have
>>> gotten to that one on my own, don't understand the internals enough.
>>> :-)
>>>
>>> - John Hobbs
>>>
>>> john velvetcache org
>>>
>>> On Tue, Aug 12, 2008 at 12:15 AM, Chris Wilson
>>> <christopher g wilson gmail com> wrote:
>>> > Here is the method I successfully use:
>>> >
>>> > I have a class called daViewMap which is derived from Gtk::DrawingArea
>>> > I use a Cairo::ImageSurface to import a 2-D array into an useful image
>>> > form
>>> > for Cairo.
>>> >
>>> > class daViewMap : public Gtk::DrawingArea
>>> > {
>>> > public:
>>> >      Cairo::RefPtr<Cairo::ImageSurface> viewSurface;
>>> >      Cairo::RefPtr<Cairo::Context> myCr;
>>> > };
>>> >
>>> > daViewMap::daViewMap() :
>>> > {
>>> >     viewSurface = Cairo::ImageSurface::create(&viewMap[0][0],
>>> > Cairo::FORMAT_A8, VIEW_MAP_X, VIEW_MAP_Y, VIEW_MAP_X );
>>> >     myCr = Cairo::Context::create(viewSurface);
>>> > }
>>> >
>>> > I perform all the cairo-based drawing using the context daViewMap->myCr
>>> > and then extract the image via a button callback:
>>> >
>>> > void exportImage(std::string filename)
>>> > {
>>> >         Glib::RefPtr<Gdk::Window> win2 = daViewMap->get_window();
>>> >         if (win2)
>>> >         {
>>> >             Glib::RefPtr<Gdk::Drawable> dra2 =
>>> > Glib::RefPtr<Gdk::Window>::cast_dynamic(win2);
>>> >             Glib::RefPtr<Gdk::Pixbuf> img2 = Gdk::Pixbuf::create(dra2 ,0
>>> > ,0
>>> > ,daViewMap->get_allocation().get_width(),
>>> > daViewMap->get_allocation().get_height());
>>> >             img2->save(filename,Glib::ustring("png"));
>>> >         }
>>> > }
>>> >
>>> > Note the use of a Pixbuf to extract the image from the drawing area's
>>> > space,
>>> > and then we use that to save it out to a file.
>>> >
>>> > Hope that makes sense...
>>> > Chris Wilson
>>> >
>>> > On Mon, Aug 11, 2008 at 5:48 PM, John Hobbs <john velvetcache org>
>>> > wrote:
>>> >>
>>> >> Hello, I apologize if this is off-topic as it deals a lot with Cairo,
>>> >> I feel it is a borderline thing.  Please feel free to send me packing
>>> >> to somewhere else if I'm wrong on that point :-)
>>> >>
>>> >> I'm trying to load an image into a DrawingArea, then put lines on it
>>> >> with Cairo and get that back out.  Is this possible or do I need to go
>>> >> figure out something with GC and Drawable?
>>> >>
>>> >> Here's the guts of the procedure so far, sorry it's big but I don't
>>> >> know how to trim it down and keep it understandable.
>>> >>
>>> >> ---------------------------------------------
>>> >> class ExampleWindow : public Gtk::Window {
>>> >>
>>> >>        public:
>>> >>                ExampleWindow (std::string path) {
>>> >>                        imagePB = Gdk::Pixbuf::create_from_file(path);
>>> >>
>>> >>
>>> >>  drawOnMe.signal_expose_event().connect(sigc::mem_fun(*this,&ExampleWindow::on_da_expose_event));
>>> >>                        add(drawOnMe);
>>> >>                        show_all();
>>> >>                }
>>> >>
>>> >>        private:
>>> >>                Gtk::DrawingArea drawOnMe;
>>> >>                Glib::RefPtr<Gdk::Pixbuf> imagePB;
>>> >>
>>> >>                bool on_da_expose_event (GdkEventExpose * event) {
>>> >>                        std::cout << "Expose Event" << std::endl;
>>> >>                        Glib::RefPtr<Gdk::Window> window =
>>> >> drawOnMe.get_window();
>>> >>                        Cairo::RefPtr<Cairo::Context> context =
>>> >> window->create_cairo_context();
>>> >>                        Cairo::RefPtr<Cairo::ImageSurface> image_surface
>>> >> =
>>> >> Cairo::ImageSurface::create (Cairo::FORMAT_RGB24,
>>> >> imagePB->get_width(), imagePB->get_height());
>>> >>                        Cairo::RefPtr<Cairo::Context> image_context =
>>> >> Cairo::Context::create(image_surface);
>>> >>
>>> >>                        Gdk::Cairo::set_source_pixbuf (image_context,
>>> >> imagePB, 0.0, 0.0);
>>> >>                        image_context->paint();
>>> >>
>>> >>                        context->set_source(image_surface, 0.0, 0.0);
>>> >>                        context->paint();
>>> >>
>>> >>                        context->set_line_width(5.0);
>>> >>                        context->set_source_rgb(0.8, 0.0, 0.0);
>>> >>                        context->move_to(10,20);
>>> >>                        context->line_to(100, 200);
>>> >>                        context->stroke();
>>> >>
>>> >>                        return false;
>>> >>                }
>>> >> };
>>> >> ---------------------------------------------
>>> >>
>>> >> I tried getting a surface from that context after the stroke() call
>>> >> and then a write to PNG:
>>> >>
>>> >> Cairo::RefPtr<Cairo::Surface> sfc = context->get_target();
>>> >> sfc->write_to_png("please_work.png");
>>> >>
>>> >> That just crashed on an expose event and I didn't bother to debug. I
>>> >> have the feeling I've gone wrong in my understanding of Cairo.
>>> >>
>>> >> So I guess what it boils down to is I'm curious if there is an easier
>>> >> path by using something in Gtkmm (which I chased my tail for a long
>>> >> time trying to find something) or if there is a way to get that drawn
>>> >> data back out of there.
>>> >>
>>> >> Thanks for any and all help :-)
>>> >>
>>> >> - John Hobbs
>>> >>
>>> >> john velvetcache org
>>> >> _______________________________________________
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>>> >> gtkmm-list gnome org
>>> >> http://mail.gnome.org/mailman/listinfo/gtkmm-list
>>> >
>>> >
>>> _______________________________________________
>>> gtkmm-list mailing list
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>>
>>
>